Amplifiers used in radio equipment have high power efficiency. Since linearity and power efficiency of an amplifier may be contradictory, various distortion compensation methods may be proposed. The distortion compensation methods may include a predistortion technique that adds, in advance, a characteristic which is the inverse of a distortion characteristic of the amplifier to an input signal of the amplifier, so as to reduce distortion created in the amplifier.
The distortion compensation methods may include a predistortion technique in which distortion compensation coefficients are stored in a lookup table (LUT) which is used to compensate for a hysteresis, such as a memory effect, of the amplifier. The distortion compensation methods may also include a technique which involves generating a predistortion signal using a Volterra series or a memory polynomial expansion.
Related art is disclosed, for example, in Japanese Laid-open Patent Publications Nos. 2007-189535, 2002-141754, and 2010-183310.